- Hematopoietic stem cells: Patients must have an adequate unpurged peripheral blood hematopoietic stem cell product, with a minimum of 2 X 106 CD34+ cells/kg available. Having a back-up of 2.0 x 106 viable CD34+ cells/kg unpurged PBSC is recommended but not required. The use of purged stem cells or autologous bone marrow as donor source is not allowed. The use of PBSC from an identical twin is allowed.